Delay device



Aug. 2, 1960 s. H. M. DODINGTON DELAY DEVICE Original Filed Aug. 28,1944 2 Sheets-Sheet 1 8 /m D F. M I A M 6 7 UV W m 9 0 x u 5 1 M y m v lC M L G wwrwm W c M KEY/N6 CIRCUIT TO OUTPUT HMPZ/Ff/EA FROM RECEIVE/iATTOPNFY Aug. 2, 1960 s. H. M. DODINGTON 2,947,954

DELAY DEVICE Original Filed Aug. 28, 1944 2 Sheets-Sheet .2

I I 28b INVENTOR. 'l/f/V H. M. DOD/N670 ATTOIWVEY -brations only.)

limited States 2,947,954 ?atented Aug. 2, 1960 DELAY DEVICE Sven H. M.Dodington, Nutley, N.J., assignor to Internatlonal Telephone andTelegraph Corporation, a corporation of Maryland Original applicationAug. 28, 1944, Ser. No. 551,470. and this application Oct. 20, B45, Ser.No.

2 Claims. (Cl. 333-30) mit return pulses or Waves of such strength,formation and time retardation as to simulate one or more ships oraircraft at some selected distance from the radio locating system.

for producing repeat pulses having means for imparting to the repeatpulses a given delay, and/or multiplication of the pulses, in responseto the received impulses.

Another object of the invention is to provide a method and means forproducing in response to radio impulses a composite pulse signal and toeffect substantially continuous change in the signal.

In accordance with my invention, I provide in a pulse repeating systemcomprised of a receiver for accepting the incoming impulse signal byheterodyning the radio frequency carrier of such signal with a locallyproduced oscillation, a delay device to produce pulses formed of acarrier at an intermediate frequency which are suitably amplified,multiplied in their response, and delayed with-respect to the incomingsignal, the produced pulses being subsequently re-transmitted, afterheterodyning the above mentioned intermediate frequency carrier with thesame locally produced oscillation in order toobtain the same outgoingfrequency for the carrier as that of the incoming signal. For obtainingthe delay and multiplication of the response pulses, the incomingimpulses, at the intermediate frequency of the carrier are applied toelectro-mechanical vibratile element such as a piezo-elect-ric typequartz crystal, having a natural frequency which has a given relation tothe said intermediate frequency and which is sufficiently damped tocover the required band width. The incoming impulse forces the crystalinto oscillation at the pulse frequency, and sets up a supersonic typewave train in a 7 liquid in which the crystal is immersed and throughwhich the wave train is propagated at the speed of sound. (For purposesof definition, the expression supersonic as used here has reference tomechanical vipositioned opposite the crystal within the liquid and inthe line of travel of the Waves set up by the crystal. .The wave trainemanating from the crystal is reflected from the surfaces at the far endof the liquid bath and thereacross.

A number of reflecting surfaces are' .30 -It is an object of theinvention to provide a device same wave shape as the voltage impulseapplied to the crystal a few microseconds before, the delay beingdependent on the distance between the crystal and the surfaces and thecharacteristics of the liquid. By using several reflecting surfaces atdiffierent distances and making use of the multiple reflectionsobtainable therefrom, it is possible to get a whole chain of repeatpulses in response to each of the impulses applied. A keying voltagewhich is triggered by the incoming impulses, may be provided forblanking out the undesirable portions of the response or repeat pulsesso that only the desired group or portion of pulses may bere-transmitted and to permit alternate operation of the transmitter andreceiver.

In order to further render the pulse repeating system to appear naturalin its effect, the so-called breathing effect, which is characteristicof indications of moving obstacles such as a squadron of ships oraircraft, is achieved in this instance by means of a variation in thelength of the path of propagation through the liquid, or alternativeshaving a similar effect. I may also provide a non-mechanical alternativefor achieving the breathing effect, by continually varying the locallyproduced beat frequency in a given slow rhythm which, when combined withthe fixed input and output frequencies of the carrier of the incomingimpulses and the outgoing repeat pulses, results in a breathing orundulating pattern of the outgoing pulse trains.

The above and other features and objects of the invention will becomeclearer upon consideration of the following detailed description of theinvention to be read in connection with the accompanying drawings inwhich: Fig. 1 is a schematic block diagram of a composite singlerepeater according to the principles of the invention;

Fig. 2 is a schematic representation of a part of the circuit of Fig. 1With the device for delaying the repeat pulses shown in longitudinalsection;

Fig. 3 is a section of an alternative folrn of a repeat pulse delaydevice, and Fig. 4, a plan view thereof;

Fig. 5 is a view in vertical section of the mechanical construction ofthe delay device of Fig. 2;

of the repeater system of Fig. l.

The block diagram of Fig. 1 shows schematically the parts of the radiorepeater system in accordance with the invention disclosed in myaforesaid copending application, Ser. No. 551,470. A two-way antenna 4is connected to a transmitter-receiver comprised of a coupling unit 5connected to an input converter 6 wherein the radio frequency or ultrahigh frequency of the carrier of the incoming radio impulses are beatdown to a supersonic frequency by heterodyning against the output of alocal oscillator 7 for application to a wide band I.F. amplifier stage8.

Connected to the output connection of the 'LF. stage 8 is an outputamplifier it which is connected to an output converter 12, wherein theintermediate frequency carrier energy, to which has been added delayedresponse or repeat pulse energy from a delay device 11 coupled to theoutput connection 9, is re-converted to the original incoming impulsecarrier frequency by heterodyning against the output of the oscillator7. The output converter 12 is connected to the coupling unit 5 feedinginto antenna 4 now functioning in its transmission capacity.

A keying circuit 13, receiving its controlling impulses from ademodulator D of the output of the input amplifier 8, delivers asuitable keying voltage both to the output amplifier 10 and to the inputamplifier 8 for blocking control thereof, so that the receiving andtransmitting functions of the apparatus do not interfere, but followoneanother with the frequency of the keying pulses. The demodulator D maybe of the type as shown, that is a.

rectifier, or it may take the form of other arrangements capable ofperforming the same function. The keying pulses supplied to the inputand the output amplifier, respectively, are shown adjacent therespective connecting leads in Fig. 1. These keying pulses may beobtained from the plate connections of a trigger type of multi-vibratorcircuit, the grid of the second tube of which has been functions of thedelay device 11 which forms the essence of this invention. Inductivelycoupled at 16, to the outward connection 9 connecting the last stage 14of the LF. amplifier 8 with the first stage 15 of the output amplifierit}, there is shown the delay device 11. The delay device comprises acontainer 17 in which there is positiQllcd a suitable electro-mechanicalvibratile means which, for e);- ample, may be a piezo-electric typequartz crystal rnersed in a liquid medium 19. At the far end of thecontainer 17 a number of reflecting surfaces 20, 21 and 22 are combinedin a single reflecting block as will be explained in detail hereinafter.

An alternative form for the delay device is shown in Fig. 3 where, inplace of a single reflecting block, reflecting surfaces are provided bya number of bi-metallic strips .23, arranged at different distances fromthe crystal and through which a heating current is applied periodicallyat 24, whereby the strips are made to buckle periodically and thus varytheir respective distances [from the crystal container and mounted onthe base 26, is an insulating block 27, on top of which is secured anelectric heating 'unitcornprising an insulating disc 28 and aceramic-member 28a having wound thereon a heating Wire 28b. The

insulating disc 28 has secured thereto a cell element 29 which is placedover the heating unit for conduction of heat. The cell element 29,together with a cell sleeve 30 of non-conducting material and a cell top31 forms an enclosed chamber at 32. A liquid medium having suitableproperties may be injected into the chamber 32 through .a filler cap 34which serves to close an opening 33 inthe .cell top 31. The filler capis provided with flexible brass bellows 42 which allows contraction andexpansion of the liquid. The inner end of the cell base 29 is formed"with an anular surface at 35 whereon is secured by means .Qfthe members36, a quartz crystal 37 mounted between two aluminum members serving aselectrical conductors and acoustic reflectors. The inside end of thecell .top .31 is formed with a series of annular steps providing therefleoting surfaces 20, 21 and 23. A pair of connecting :members 38 and39 extending through the insulating block 27 serve to conduct heatingcurrent to the wire 28b where- .by the temperature of the liquid in thecell may be varied as desired, as well as to conduct electric impulseenergy-to the crystal through the cell member 29, which engages:connection 38, the return being established through the .;other side ofthe crystal which is ground through the'cell top 31 and the container orshell 25.

Fastening bolts 40 and 41 are shown securing the insulating member 27,and thereby the entire cell assembly -.to the base 26.

Thomethod of obtaining echo or repeatpulses which are-properly delayed.and multiplied in response to in- :comingimpulses will now be describedin .connection twith Fig. 6.

The incoming pulse, the carrier of which has been heterodyned to anintermediate or supersonic frequency in the input converter, having theform as shown in graph a is applied to the quartz crystal 18 (Fig. 2).The natural frequency of the crystal may be for instance /3 that of theLF. and the crystal is sufiiciently clamped to cover the-required bandwidth. The in coming impulse forces the crystal into oscillation at thepulse frequency and sets up a wave or pulse train in the liquid whichtravels through the liquid at the speed of sound. This wave train isreflected from the surfaces 29, 21 and 22 and, on returning through theliquid, strikes the crystal and induces a voltage thefein which ll a suan i ll the Wa e Sh re a he vo ta e er.- Plis t0 he cr sta by he nc mipu e. t be sep rated therefrom by a few microseconds representing thedifference in point of time between the application of the impulses tothe crystal and the inducement of the repeat pulse voltages in thecrystal by the reflected supersonic pulses. The combined pulse form dueto the multiple reflections is shown in graph b, the delay due to thetime of travel from the crystal to the surfaces and back being indicatedby the interval r It is obvious, of course, that the reflecting surfacesmay be varied in respect to their number and spacing so that varioustYPfiS of composite wave shapes may be obtained.

As indicated in Fig. l the keying circuit 13 will be triggered by thedemodulated incoming pulse to. set up a keying impulse of the type shownin graph c which is effective in cutting off any undesired portions ofthe reflected pulses. The shape of the keying pulses, which of coursemay take other forms as desired, in this instance is such that maximumgain is obtained toward the end of the repeat pulse wave so as tocompensate for the smaller reflections obtained at that point. The formof the pulse as finally re-transmitted in response to the originalincoming pulse is shown in graph d. It will be noted that the originalimpulse is not re transmitted, the beginning of the keying pulse beinglocated to take into consideration the time delay r and having such aform as to reduce the amplitude of any portion of the retransmittedoriginal pulse.

The delay in the liquid depends on the velocity of sound characteristicfor the particular liquid .choscn, water, for instance, giving a delayof about 7 microseconds per centimeter. Most other liquids will give aslightly greater delay. In this particular instance, and for theapplication suggested, a liquid having a low freezing point and whoseattenuation of the wave train is relatively high, should be chosen. Theliquid should also be non-inflammable.

In addition to generating the complex wave form in response to theincoming signal, it is also possible to obtain a random variation of theresultant wave form to simulate the so-called breathing produced by atrue radio location system reflection. This effect may be had byintroducing heat by means of the electric heating element 28 (Fig. 5).The resulting temperature gradient across the liquid produces arelatively substantial random change in the velocity of propagation in.dif ferent parts of the liquid, resulting in greater .and lesser delayof the reflected pulses. The envelope of the ,resultant complex wave ofgraph :1 consequently is modem undulate and breathe in a manner notunlike that of a true radio locator reflection of a squadron of ships oraircraft in motion. In the alternative construction .of the delay devicein Figs. 3 and 4, wherein metallic strips serve as reflecting surfaces,such strips are .made to buckle and move in response to heatingcurrents. Another method for simulating the breathing effect isindicated in'Fig. l where the local oscillator is shownto be variable,thus producing with the radio .frequency carrier of the incomingimpulses an intermediate frequency carrier impulsewhich slowly variesinits wave shape in accordance with therhythm of variation in thefrequency of the local oscillator.

In view of the fact that crystal harmonics necessitate a very largeamount of amplification, it is necessary to use crystals at the highestpossible frequency consistent with reliability. Since the supersonicfrequency applied to the crystal in this case is eflective in producinga wave having a length measured in hundredths of a millimeter in mostliquids and only somewhat larger in most metals, reflecting systems tomodify the response within a useful band must, therefore exhibitaccuracies of a fraction of the wave length in liquids. The choice,therefore, was made to load the crystal with only the liquid, and toemploy several crystals to cover the requisite band, using electricalcircuits to compensate for inequalities between crystals.

While I have shown and described principles of my invention inconnection with specific apparatus, it will be understood that the delaydevice may be considerably varied with respect to material used in theconstruction thereof as well as in the particular arrangement of parts.It will be understood, therefore, that the specific apparatus hereinshown and described is to be regarded as illustrative of the inventiononly and not as limiting the scope thereof.

I claim:

1. A device, comprising means defining a chamber, a piezo-electriccrystal having a given resonant frequency located in said chamber, meansforming a plurality of supersonic pulse reflecting surfaces in saidchamber, means for applying and taking off electrical impulse energywith respect to said crystal, a fluid medium in 6 said chamber providinga path of propagation for supersonic pulses between said crystal andsaid reflecting surfaces, an element for heating said fluid mediumwhereby the propagating characteristics of said fluid medium may bevaried, and means to apply an electric heating current to said element.

[2. A device for producing a composite wave formation comprising meansproviding a chamber containing a medium adapted to convey mechanicalvibration, means to initiate a mechanical vibration in said medium, aplurality of successively spaced bi-metallic elements having reflectingsurfaces for multiple reflection of vibrations established in saidmedium, and means to apply heating current to said elements when theelements are in a certain condition to cause them to flex, whereby thereflecting positions of said surfaces are changed.

References Cited in the file of this patent UNITED STATES PATENTS1,858,931 Longevin et al. May 17, 1932 2,248,870 Longevin July 8, 19412,263,902 Percival Nov. 25, 1941 2,405,591 Mason Aug. 13, 19462,407,294- Shockley Sept. 10, 1946 OTHER REFERENCES Article entitled,Ultra-sonic Measurements of the Compressibility of Solutions and ofSolid Particles in Suspension, published in Bureau of Standards-Journalof Research, vol. 8, January 1932, pages 79-96.

